Hydrophone with frusto-conical hollow carbon elements



Jan. 22, 1963 R. 1-. SOREL 3,075,170

HYDROPHONE WITH FRUSTO-CONICAL HOLLOW CARBGN ELEMENTS Filed June 4, 195B 25 2f 3% 3/ if r m MW United States atent HYDROPHQNE WITH FRUSTG-QIGNICAL HQLLOW CAREsEN ELEMENTd Raymond T. Sci-cl, River Road, RED. 2, Mystic, (joint. Filed .iune 4, 1958, Ser. No. 739,951 1 Claim. (Cl. 34tl-13) (Granted under Title 35, US. Code (E52), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the pay ment of any royalties thereon or therefor.

This invention relates to hydrophones and particularly to carbon hydrophones. Presently used hydrophones commonly employ magnetostrictive or piezo-electric elements which provide small voltages that are amplified until they can perform useful functions. A disadvantage of such hydrophones is that the need for amplification increases the complexity and cost of the devices and reduces their reliability. In addition the characteristics of the elements make them unsuitable at very low frequencies.

An object of this invention is to provide an improved carbon hydrophone, with which the overall resistance of the device can be easily and inexpensively changed; with which the sensitivity and impedance remain constant over a wide frequency range, especially at low frequencies; which will respond to frequencies having periods of several seconds or even minutes as well as to the higher frequencies to which hydro-phones should be responsive; which will itself be an amplifier capable of substantial power gains; which is directional in its responses; which has minimum of self noise; which has good discrimination in isotropic noise; which has improved mechanical impedance match to water; which has a relatively high sensitivity; which is useful for acoustic mines in that it can be made to respond to both acoustic and pressure signatures; with which the electrical impedance is constant with frequency; with which the impedance is practically purely resistive; with which the high output reduces the number of stages of electronic amplification necessary and makes electronic amplification unnecessary in some cases; which has simple and modest power requirements; and which will be relatively simple, compact, durable, practical and inexpensive in construction.

Other objects and advantages will be apparent from tie following description of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

The drawing is a sectional elevation of hydrophone constructed in accordance with the invention and illustrating an embodiment thereof.

In the embodiment of the invention illustrated, the hydrophone includes a disk 23 of non-conducting material such as fiber-glass or formica, which is electrically non-conducting, rigid, and capable of holding its rigidity under stress. An inertia loading weight 24 is disposed against one face of the disk 23 and detachably secured thereto by having a reduced stem on the weight 24 threaded into an aperature in the disk 23. The loading weight is tapered toward its free end, and circular in cross section so as to be frusto conical in shape. This inertia loading weight is of metal, and telescoped snugly upon it and upon each other are a plurality of frusto conical elements or sleeves 2a of suitable carbon material. Disposed between the successive elements 26 are frusto conical thin sleeves 27 of metal which separate the adjacent faces of the frusto conical elements and are provided with apertures 27:: from face to face except for the outermost sleeve 27 which does not have any apertures. These successive frustums of cones 26 and 27 are super-posed until the larger base ends thereof cover the contiguous base of the disk 23.

Another disk 28, similar to the disk 23 but slightly smaller in diameter, abuts against and is coextensive with the free ends of the members 26 and 27. A frusto conical thin rubber boot 29, which serves as a sound transparent cover, fits snugly over the exterior of the group of elements 26 and 2'7, with one end encircling and snugly fitting the periphery of the disk 23 and the other end encircling and snugly fitting the periphery of the smaller disk 28. A suitable adjustable clamp 36 extends around the periphery of the disk 28, over the end of the boot 29, so as to clamp the end of the boot tightly to the periphery of the disk 28 and provide an impermeable seal therewith and to hold the disk 28 against the contiguous ends of the elements 26 and 27.

A water-prom molded rubber boot 31 is secured against the other end face of the disk 23 by its flanges 32 which extend in telescopic relation over the periphery of the disk 23 and the adjacent end of the boot 29, and another adjustable clamp 33 surrounds the flange 32 and when. this clamp is tightened, it provides an impervious seal between the boots 29 and 31 and the periphery of the disk 23. A pair of insulate-d wires 34 and 35 are molded in the stem 36 of the boot 31 so as to extend to the inner face of the boot 31, where one wire 34- is secured to the integral metal stem 25 of the inertia loading weight 24, and the other wire 35 passes near the periphery of the head of the boot and there emerges and passes through a small oblique passage 37 in the disk 23 where the wire is electrically secured to the outer-most frusto-conical metallic member 27.

These spacer members 2.7 which are between the members 26 have their face areas which abut members as of considerably less areas than the face areas of the carbon members 26 against which they abut except the outermost spacer member which has the same face area as the adjacent carbon member against which it abuts. The two disks 23 and 2%, with the boots 29 and 31, form an impervious enclosure in which the carbon frusto-conical elements are housed in face to face relation, and sound waves impinging against the sound transparent boot 29 on the side of this housing will cause the outermost frustoconical carbon member 26 to move against the next adjacent one, and progressively on to the innermost one, thus varying the resistance between the frustum shaped carbon elements and the spacers from the outermost Y rustum to the innermost one, as the sound waves vary. This hydrophone is thus also directional in that it is responsive to sound waves striking the boot 29 in a direction crosswise of the common axis of the elements 26 and 27.

A hydrophone which is trying to discriminate between a weak distant signal and very close noise sources has an advantage if the close sources do not afifect the hydrophone materially. If the local noise field is large enough, it may appear to the hydrophone that the noise arrives simultaneously from all directions. The carbon disk hydrophone or the hydrophone using the carbon frusto-conical elements, changes the resistance for signals coming from one direction while pressures from signals arriving simultaneously from other directions are mechanically cancelled out. Conventional piezoelectric or magnetostrictive units produce outputs regardless of the mode that the unit is excited. These units usually rely on the sensitivity of a particular mode to give directional characteristics, or an array of units is used, with proper phasing, to give directional characteristics.

For the cone frustum construction of the carbon elements, the sensitivity pattern for this configuration is doughnut shaped, and therefore this configuration is sensitive to sounds in all directions except those parallel to the axis of the cone.

The inertia of the loading weight causes the sides of the carbon cone frustums to move when a sound wave comes from some direction at right angles to the cones. The sound pressure coming from one side causes the sides of the cone at that side of the axis to compress and reduce the resistance, and at the same time the sides of the cones on the other side of the axis will be moved apart so as to reduce the resistance, but unless the sound pressure travels through the cones instantaneously, which is a physical impossibility, the reduction in resistance on the said other side of the axis will not arrive soon enough to subtract from the increase in pressure on the sides first engaged by the sound waves. The low frequency response of the cone frustum will be limited to a frequency which is so low that the change in acoustic pressure coincides with the speed of sound through the cones.

Frustums are used instead of cylinders to make a snug fit between elements without the need for maintaining precise dimensions. The illustrated embodiment of this invention has an improved mechanical impedance match to the water. Hydrophones according to this invention have wide uses including the use in fathorneters, sonar devices, acoustic mines and underwater telephones. This type of hydrophone is particularly useful in connection with acoustic mines. Mine sweeping gear can explode most acoustic mines by towing a noisemaker on a paravane. An acoustic mine with a carbon element hydrophone in accordance with this invention can be made sweep proof. spouse of this new type of carbon element hydrophone, it can be made to close a circuit alerting it to noise signals, only after the very low frequency pressure signature (pressure variation with respect to time or frequency) of a large ship is sensed. In other words, the hydrophone would refuse to listen to noise unless a large ship came within range, where the movement of the water caused by the displacement of the hull caused the mine to become alerted. While such mines are already in existence,

they are more complicated than those using a carbon element hydrophone in accordance with this invention, because they usually have a separate pressure signature (pressure variation with respect to time or frequency) sensing element, and the hydrophone output has to be amplified to actuate the mine. Hydrophones made in accordance with this invention are easily disassembled by removing the boot 29. It will be understood that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in Because of the very low frequency reorder to ex lain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claim.

I claim:

A carbon hydrophone for inclusion in a hydrophone utilization circuit comprising an electrically non-conducting rigid disk, a metallic frusto-conical inertial member detachably affixed centrally of said disk with its tapered tree end extending away from said disk, a group of substantially rigid hollow frusto-conical carbon elements with substantially broad faces as compared to their thickness arranged coaxially in telescoping relation on said member,

thin frusto-conical metallic sleeves interposed in abutting face to face relation between adjacent elements, said sleeves having smaller face areas than those of the element against which they abut, a metallic outer frustoconical sleeve abutting the outermost element and of a face area approximately equal thereto, said sleeves and carbon elements covering substantially all of the face of said disk against which the ends of said elements and sleeves abut, a second electrically non-conducting disk abutting and covering substantially all the free ends of said elements and sleeves, a frusto-conical boot of sound transparent and water impervious material extending between said disk and said second disk, sealed thereto in abutting relation with said outer sleeve, a water impervious end boot extending across and covering the face of said disk opposite said elements and sealed thereto, a pair of wires extending through said end .boot, sealed therein, one of said wires attached to said member and the other passing through said disk and attached to said outer sleeve whereby said hydrophone is water impervious and compressional waves impinging on said frusto-conical boot will be transmitted to said elements.

References Cited in the tile of this patent UNITED STATES PATENTS 380,925 Phelps Apr. 10, 1888 1,544,786 Walker July 7, 1925 1,584,613 Cornstock et al. May 1 1, 1926 1,829,489 Mularkey Oct. 27, 1931 2,405,226 Mason Aug. 6, 1946 2,405,604 Pope Aug. 13, 1946 2,515,867 Fuller July 18, 1950 2,813,181 Seavey c Nov. 12, 1957 2,830,202 Feinstein Apr. 8, 1958 

